Towards More Reliable PbO-SiO2 Based Slag Viscosity Measurements in Alumina via a Dense Intermediate Spinel Layer

The goal of this work is to accurately measure the viscosity of an industrial secondary copper smelting slag. Established literature commonly performed such measurements in non-inert labware, such as alumina. Despite the fact that the dissolution of alumina into the slag was addressed as a source for errors, a comprehensive analysis of how this interaction affects the measurement reliability is hitherto lacking. Furthermore, the type of dissolution (direct or indirect) will influence the interaction kinetics. This work aims to verify a possible relation between the dissolution and viscosity measurement reliability. For this purpose, the infiltration depth during and time stability of four different slag ( PbO-SiO 2 -CaO-Al 2 O 3 -ZnO-Fe 2 O 3 ) viscosity measurements were analyzed. Both in-situ viscosity measurements and post mortem SEM images of the interface were therefore analyzed. It was observed that a multiphase interfacial layer was formed upon alumina dissolution. This layer consisted of a spinel intermediate layer and an enclosed interfacial slag. EDX measurements confirmed the difference between the latter layer’s composition and the bulk slag. Samples with a high interfacial slag viscosity yielded a dense spinel layer. As a result, alumina dissolved indirectly and more reliable viscosity measurements were obtained that were more stable over time. While samples with a low interfacial slag viscosity yielded a discontinuous spinel layer and therefore alumina could dissolve fast into the bulk slag, resulting in more unreliable viscosity measurements that varied over time.